1. Field of the Invention
The present invention is related to an electroluminescent light emitting element which uses light emitted by electroluminescence, and a manufacturing method thereof.
2. Description of the Related Art
Electroluminescent light emitting elements are expected to have applications to flat panel displays. In applications to displays, it is important that the emitted light have high luminance and high luminous efficacy.
FIG. 1 shows the structure of a related art electroluminescent light emitting element. In this structure, a transparent electrode layer 32, a light emitting layer 33 and a metal electrode layer 34 are laminated in that order onto a glass substrate 31. When an electric field is applied between the transparent electrode layer 32 and the metal electrode layer 34, light is emitted from the light emitting layer 33 by electroluminescence. This emitted light is emitted into the air 30 after passing through the transparent electrode layer 32 and the glass substrate 31.
However, there is a large difference between the index of refraction of the glass substrate 31 and the index of refraction of the air 30, and when the incidence angle from the glass substrate 31 to the air 30 is greater than or equal to the critical angle for total reflection, the light emitted from the light emitting layer 33 can not be emitted into the air 30. Because the index of refraction of a glass substrate is normally about 1.5, the critical angle from the glass substrate 31 to the air 30 is approximately 42 degrees. Any light propagating inside the glass substrate 31 having an incidence angle greater than or equal to this critical angle will be confined inside the glass substrate 31 and the like. Due to the effect of this confinement, a large portion of light can not be emitted into the air 30 from the glass substrate 31. Consequently, there has been a desire to reduce as much as possible the effect of confinement to the glass substrate in order to emit electroluminescent light efficiently into the air.
Further, because the light emitting layer 33, the transparent electrode layer 32, the glass substrate layer 31 and the air 30 all have different indexes of refraction, reflected light is created due to the difference in the index of refraction at each of the boundaries from the light emitting layer 33 to the transparent electrode layer 32, from the transparent electrode layer 32 to the glass substrate 31, and from the glass substrate 31 to the air 30. When reflected light is created, because the electroluminescent light is attenuated, it is not possible to emit light efficiently into the air. Consequently, there has been a desire to reduce as much as possible the number of times that the electroluminescent light passes through a medium having a different index of refraction in order to emit electroluminescent light efficiently into the air.